1. Field of the Invention
The present disclosure generally relates to compositions and methods for treating subterranean formations. More particularly, the present disclosure relates to a crosslinking system for increasing the viscosity of a well servicing fluid.
2. Description of the Related Art
In the oil and gas, water well, and injection well industries, boreholes are drilled into subterranean formations and certain fluids may then be introduced therein. A number of different types of fluids are used in drilling, completing, and working over an oil, gas, water, and/or injection well completed in a subterranean formation. Subterranean formations can be any buried rock structure where the flow of fluids into or out of the formation is desired. These formations may include, but are not limited to, sandstones, limestones, dolomites, shales, coal beads, and diatomeatous earth. The subterranean formation may produce oil, gas, water, condensate, or any combination thereof.
The subterranean formation may also be used for the injection of fluids. The injected fluid may be a water based fluid, brine, a polymer solution, gas, or CO2. The flow of fluids into and out of the formation may be through natural permeability, enhanced permeability, natural fractures, manmade fractures, or geologic features, such as seams and faults.
A well servicing fluid can be any fluid used in drilling, completing or workover operations performed in the subterranean formation. These can include, but are not limited to, drilling fluids, drill-in fluids, fracturing fluids, gravel packing fluids, completion fluids, workover fluids, stimulation fluids, chemical treatment fluids, perforating fluids, well cleanout fluids, spacer fluids, polymer flooding fluid, a kill fluid, or a lost circulations fluid.
In a number of cases, the well servicing fluid needs a relatively high viscosity to perform a desired function. The function may include, but is not limited to, particles suspension and transport, fluid leakoff control, pressure buildup, altering the injection profile, and any combination of these. Generally, the viscosity is gained by the addition of a polysaccharide, such as guar and any of its derivatives. Even greater viscosity is achieved by adding a material referred to in the art as a crosslinker. A crosslinker is a chemical compound that is capable of forming a chemical link between a site on one polymer with a site on another polymer. This crosslinking can increase the viscosity (or apparent viscosity) several fold, perhaps even as high as hundreds of fold increase.
Boron based compounds are well known in the art as useful for crosslinking polysaccharides. Illustrative examples of boron compounds include borax and boric acid. Some naturally occurring boron containing minerals are also useful as crosslinkers. These minerals, illustratively including ulexite and colemanite, have the added advantage of crosslinking the fluid in a delayed manner.
Having some delay in the crosslinking time can be advantageous in reducing the amount of pressure required to convey the fluid down the well casing, tubing, coiled tubing, or drill pipe. The reduction in surface pumping pressure can allow a higher pumping rate (measured in barrels per minute, bpm) where the higher pumping rate may increase the efficiency of the action of the well servicing fluid. For example, in hydraulic fracturing a high pumping rate may be desired in order to get the designed width, length, or height of the fracture, or to carry proppant a given distance from the wellbore.
As stated above, the boron containing minerals, such as ulexite and colemanite, function as crosslinkers and do so with some delay in the onset of crosslinking, especially when compared to the substantially instant crosslinking from the more water soluble boron compounds, such as borax or boric acid. Even further delays have been seen with these mineral based crosslinkers when they are suspended in oil based fluid system. The addition of this oil based suspension system to a crosslinkable polysaccharide solution has a delay in crosslink time that is materially longer than that observed with adding the mineral based crosslinker as a dry powder. An oil based suspension of a boron mineral generally comprises a boron mineral powder, an oil, a clay for suspension, a surfactant, an activator. Although a material delay is seen with this type of crosslinker suspension package, the use of clays is generally undesirable since it can result in damage to the conductivity of the fracture or cause formation damage.
Water based suspension packages have been developed that may be formulated, for example, with water, ethylene glycol, xanthan or diutan, an acid, and ulexite. Again, these suspensions give the desired delay in crosslink time, but there can be issues with degradation of the xanthan or diutan with time, limiting shelf life of the product.
Thus, there is a need for a suspension system for a boron containing mineral powder without the limitation and disadvantages of those know in the art.